Zone plate radio transmission system



EFSO -MSB June 15, 1965 1.. F. VAN BUSKIRK 3,189,907

ZONE PLATE RADIO TRANSMISSION SYSTEM Filed Aug. 11, 1961 INVENTOR.

LYMAN F. VAN BUSKIRK ATTORNEY.

3,189,907 ZONE PLATE RADIO TRANSMISSEON SYSTElt'i Lyman F. Van Euskirk,211-A Byrnos, China Lake, Calif. F iled Aug. 11, 1961, Ser. No. 131,6256 Claims. (Cl. 343-753) (Granted under Title 35, US. (lode (1952), see.266) The invention herein described may be manufactured and used by orfor the Government of the United States of America for governmentalpurposes without the payment of any royalties thereon or therefor.

This invention relates to a directional radio transmission system andmore particularly to a zone plate apparatus which provides a radiofrequency antenna with beam width quality comparable to paraboloids, butof much lower cost and easier construction, and which is capable ofsimultaneous transmitter-receiver usage.

The zone plate is a diffraction device and comprises an arrangement ofconcentric rings or zones of metallic or electrically conductingsurfaces and non-metallic or nonconducting bodies or surfaces arrangedin a plane. The central portion of the zone plate may be conducting oropaque, so as to reflect radiation, or it may be non-conducting ortransparent, so as to transmit radiation, and the zones are arrangedconcentrically around the central portion in alternation. An interestingcharacteristic of the zone plate is that each point of a transparentzone nited States Patent which receives radiation acts as a secondarysource of radiation which emits a spherical wave. If the zones aredesigned to be of such diameters that radiation from all the transparentzones arrives in phase, there will be constructive interference whichwill be greatest at a focal point located at a distance from the zoneplate equivalent to the designed focal length of the zone plat Thisrequires that the distance from the focal point or focus to the edges ofthe successive zones be integral multiples of a half-wavelength, 2. Theradii of the zones may be calculated; see IRE Transactions on Antennasand Propagation, May 1961, volume AP-9, No. 3, pages 319 320, The ZonePlate as a Radio-Frequency Focusing Element, or determined graphically.The focusing action of the zone plate is independent of whether thecentral portion is opaque or transparent; that is, the focusing actionsof complementary zone plates are identical. This means that a given zoneplate has a focus for reflection as well as transmission since theopaque or metallic rings are conducting.

It is an object of the present invention to utilize the characteristicsof the zone plate to provide a radio frequency antenna.

Another object is to provide an antenna for simultaneous transmissionand reception using a zone plate.

A further object is the provision of a tracking antenna utilizing a zoneplate for telemetering.

A still further object is to provide an astronomical radio telescopeusing a reflecting zone plate.

According to one feature of the present invention, antenna feeds arelocated at the foci of the zone plate, one feed may be at a differentfrequency than the other or it may add to the same frequency.

According to another feature of the invention, a transmitting antennafeed may be located at one focus of a zone plate and a receiving antennafeed at the other focus.

According to still another feature of the invention, a zone plate withantenna feeds is gimbal-supported for tracking a moving object andreceiving telemetering information therefrom.

According to a further feature of the invention, a moving antenna feedis employed with a reflecting zone plate and ground plane for trackingcelestial bodies.

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Other objects, features and many of the attendant advantages of thisinvention will become readily appreciated as the some become betterunderstood by reference to the following detailed description whenconsidered in connection with the accompanying drawings wherein:

FIG. 1 is a view schematically illustrating one form of zone plate witha pair of antenna feeds;

FIG. 2 is a view schematicallyillustrating another form of zone platehaving associated therewith a ground plane and a movable antenna feed;

FIG. 3 is a view schematically illustrating a zone plate of ellipticalform with transmitting and receiving antenna feeds providing forsimultaneous transmission and reception; and

FIG. 4 is a view illustrating the layout of a zone plate on a radornesurface.

. Referring now to the drawings, wherein like reference charactersdesignate like or corresponding parts throughout the several views,there is shown in FIG. 1 a planar zone plate 11 which comprises acircular non-conducting or transparent central portion or zone 12.Arranged concentrically about central portion 12 are rings or zones 13 fmetallic, electrically conducting or opaque material, and non-conductingor transparent rings or zones "14, theri'ngs or zones being circular andarranged in alternation. Disposed on the central axis of the zone plate,illustrated by dotted line A, are a pair of antenna feeds 15,16, antennafeed 15 being disposed at the focal point or focusof the zone plate 11on the front side of the plateand antenna feed 16 being disposed at thefocal point or focusof the zone plate on the rear side thereof.

The zone plate maybe made in various ways. One way is to cement aluminumfoil to Plexiglas, lay out the rings or zones on the foil, then cut andpeel away the unwanted foil. Different types of feed antennas may beemployed; two types were useda straight dipole above a ground plane anda turnstile type in which the arm were drooped toward the ground plane.

Antenna feed 1-5 may be focussed to a different frequency than antennafeed 15 or may add to the same frequency. Or antenna feed 16 may be atransmitting or radiating element while antenna feed 15 is a receivingelement.

Zone plate 11 is secured to a support means such as bar 17, or the like,which is journaled for rotation in bearings 13 carried by frame 19having a shaft 21 journaled for rotation in bearings 22 mounted in asupport structure 2 2 which is secured to a base 24. Zone plate 11 isthus supported for rotation about an axis perpendicular to its centralaxis A and for rotation about the axis of shaft 21 whereby it may bepositioned as necessary to track a moving object for receipt oftelemetering information therefrom and/ or transmitting commandsthereto.

Turning now to FIG. 2, there is shown a reflecting zone plate 31 whichis complementary to zone plate 11, that is, its central circular portionor zone 32 is metallic or opaque and the transparent rings or zones 33and opaque rings or zones 34 are concentrically arranged around opaqueportion 32. Such a zone plate may be used in an astronomical radiotelescope by making the plate of sufficiently large diameter andsupporting it spaced from the ground or other plane surface 35 by abouta quarter wavelength, M4, or odd multiples thereof, and arranging anantenna feed 36 for movement generally in the surface of a sphere at theend of a radius 37. Radius 37 is equivalent in length to the focallength of the zone plate 31 and is moved about to pick up radio signals;for example, signal 38 emanating from a celestial body 39. When antennafeed 36 is located on the central axis of the zone plate it will be atthe focal point or focus of the plate.

The radiation that is reflected from the opaque zones *----32, and 34will undergo a 180 phase change.

The radiation that passes through the transparent zones 33 travels aquarter wavelength to the ground plane 35, undergoes a phase reversalupon reflection from the ground Plane, and returns a quarter wavelengthto the plane of the zone plate, whereby the portions of the radiationreflected by the opaque zones and the ground plane are in phase at thefocal point of the zone plate.

One manner of supporting antenna feed 36 is to mount it for movement onan arch which is itself movable about the zone plate as shown on page320 of the aforementioned IRE publication. However, any other meansproviding for similar movement of the antenna feed 3-5 would serve aswell.

FIG. 3 illustrates a zone plate antenna for a two-way communicationssystem providing for simultaneous transmission and reception of radiosignals. The system con"- prises a planar zone plate 41 made up oftransparent zones 42 and opaque zones 43, which are elliptical ratherthan circular, and a transmitting antenna feed 44 and a receivingantenna feed 45. Zone plate 41 may be supported after the fashion of thezone plate in FIG. 1, or in any other suitable manner, and is disposedso that the long axis of the ellipse is at an angle of 45 with respectto a line 46 passing through its center and extending from antenna feed44 to a remote station (not shown), antenna feed 44 being located at thefocal point of the zone plate. Antenna feed 45 is located on a line 4 7which is perpendicular to line 46 at the center of the zone plate and atan angle of 45 with respect to the long axis of the ellipse. Thus, thedisposition of the zone plate 41 is such that the long axis of theellipse is contained in the plane defined by lines 46 and 47.

The projection of the elliptical zone plate 41 on a plane perpendicularto line 4-5 and passing through the end of the long axis of the ellipsenearest antenna feed 44 is in effect a circular zone plate having afocal point coincident with the location of antenna feed 44. Similarly,antenna feed 45 is at the focal point of the projection of the zoneplate in a plane perpendicular to line 47 and passing through the nearend of the long axis of the ellipse.

In operation, transmitting antenna feed 44 radiates signals, some ofwhich are reflected by the opaque zones and some of which are diffractedby the transparent zones i into a beam directed at the remote station(not shown). Some of the signals from the remote station (not shown)beamed at the communications system are reflected by the opaque zonesand focusscd at the receiving antenna feed 45. By selecting properfrequencies, simultaneous transmission and reception may take place.Additionally, an antenna feed 48 may be located at the focal point online 47, but on the side of the zone plate opposite to antenna feed 45,to receive the signals from antenna feed 44 which are reflected by thezone plate for purposes such as monitoring. Large ground planes 49 maybe located at antenna feeds 44, 45 and 48 to enhance the efliciency ofthe system.

Although the zone plates described so far are planar, there is norestriction to a plane surface. The graphical layout technique may beemployed to lay out a zone plate 51 on any surface, for example, on anaircraft radome 52, shown in PEG. 4. The zone plate 51 comprisestransparent zones 53 and opaque zones 54 of metallic foil or the like,arranged in alternation. An antenna feed 55 is located at the focalpoint of the zone plate and incident radiation is diffracted by thetransparent zones and focussed at the antenna feed. In laying out zoneplate 51 on radome 52, successive radii R are generated such that thesegmented distances 56, 5-6, and so on, from the antenna feed 55 to thezone edges to a wave plane 57 differ by half Wavelengths, M2.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is:

1. In combination, a zone plate, an antenna feed on one side of saidzone plate at the focus thereof for transmitting beamed radio signals,said zone plate being disposed at an angle to said beamed radio signals,and an antenna feed on the other side of said zone plate at the focusthereof for receiving radio signals beamed at the zone late from aremote station.

2. In a two-way communication system adapted for transmission andsimultaneous reception, a zone plate, an antenna feed on one side ofsaid zone plate for transmitting high frequency energy beamed at aremote station, said zone plate being disposed at an angle of 45 withrespect to the direction of transmission, and an antenna feed on theother side of said zone plate for simultaneously receiving highfrequency energy beamed at the zone plate from the remote station.

3. The system of claim 2, wherein said second-named antenna feed is on aline passing through the center of the zohe plate and perpendicular tothe direction of transmission of-., the high frequency energy.

4. The system of claim 3, wherein the zone plate is in the form of anellipse and the long axis of the ellipse lies in the plane defined bysaid line and the direction of transmission of hi h frequency energy.

5. The system of claim 4, wherein a third antenna feed is associa nedwith said zone plate, said third antenna feed being disposed on the sameside of the zone plate as said first-named antenna feed but on the lineextending through the center of the zone from said second-named antennafeed.

6. The system of claim 5, wherein ground planes are associated with saidantenna feeds.

References Cited by the Examiner UNITED STATES PATENTS 2,043,347 6/36Clavier et al 343909 2,169,553 8/39 Bruce 343753 X 2,412,202 12/46 Bruce343--91O X 2,976,533 3/61 Salisbury 343755 FOREIGN PATENTS 1,004,62211/51 France.

HERMAN KARL SAALBACH, Primary Examiner.

2. IN A TWO-WAY COMMUNICATION SYSTEM ADAPTED FOR TRANSMISSION ANDSIMULTANEOUS RECEPTION, A ZONE PLATE, AN ANTENNA FEED ON ONE SIDE OFSAID ZONE PLATE FOR TRANSMITTING HIGH FREQUENCY ENERGY BEAMED AT AREMOTE STATION, SAID ZONE PLATE BEING DISPOSED AT AN ANGLE OF 4K* WITHRESPECT TO THE DIRECTION OF TRANSMISSION, AND AN ANTENNA FEED ON THEOTHER SIDE OF SAID ZONE PLATE FOR SIMULTANEOUSLY RECEIVING HIGHFREQUENCY ENERGY BEAMED AT THE ZONE PLATE FROM THE REMOTE STATION.